I think my drive shaft has a leak.

[audiomick]

I've had the rear end out recently. Started out as "having a look" and ended up with new wheel bearings, swing-arm bearings, spacer in the wheel between the bearings, getting the rear shock serviced, a new axle, and a replacement shaft because one of the uni joints was faulty and I got a replacement shaft quickly and cheaply.

 

But....

I put the shaft in with well-greased uni joints but not much grease in the spline that compensates for the changes in length that happen as the swing-arm goes up and down. Today, I tried to grease that part of the shaft via the grease nipple on the shaft. I am not talking about the nipples on the uni joints, just to make that clear.

After I figured out how to use the grease gun such that grease actually went in to the nipple, I thought I was doing well. And then I saw that this was happening:

 

 

I was expecting to see grease appear sooner or later at the join between the two parts of the shaft. Instead, it came out through the yoke towards the uni joint.

 

It is apparent that the rearwards part of the shaft was bored out and machined to create the spline that the forwards part of the shaft mates in to. Looking at the yoke on the shaft side of the rearwards uni joint, it is clear that there is a bung there to seal off the hole.

 

Apparently this bung is not sealed on the shaft that I have in the bike now.

 

So, the following questions:

Has anyone else seen this happen?

How bad is it? Do I have to assume that as a result of the weak spot, the spline is not being sufficiently greased via the nipple. or can I ignore the problem?

Is it possible that I sprung the bung myself by pumping too much grease in? I really can't imagine that this might be the case...

[docc]

You cannot feel any "play" or looseness between the rear yoke and rear portion of the shaft? (That would be * bad * )

Most of these yoke/shaft junctions are welded up tightly. So much so, that too much grease in the shaft connection can lock/impede normal shaft sliding movement. Looks like yours has some "relief" for that area . . .

[MartyNZ]

There's a  hole in the back end of the shaft to allow excess grease to escape from inside. If that hole was blocked, then suspension movement would break something. Grease will cause a hydraulic lock.

[audiomick]

3 minutes ago, docc said:

You cannot feel any "play" or looseness between the rear yoke and rear portion of the shaft?

No, I don't believe so.

The shaft is one that I got from someone in the German forum that I trust implicitly. The original shaft in my Le Mans had a dud uni joint. Changing the uni joint got complicated, so I took the replacement shaft. It has allegedely only about 30,000 km, although the mileage should not have any bearing on the issue in question. I think.

I'm really bloody frustrated, actually. I went to have a "quick look" in July, and the bike has not been rideable since. I thought I was on the way to getting it going again, and now this...

[docc]

2 minutes ago, MartyNZ said:

There's a  hole in the back end of the shaft to allow excess grease to escape from inside. If that hole was blocked, then suspension movement would break something. Grease will cause a hydraulic lock.

Makes me wonder how many of these "holes" get blocked?

I thought that space as closed off . . .

[audiomick]

6 minutes ago, MartyNZ said:

There's a  hole in the back end of the shaft to allow excess grease to escape from inside.

Thanks Marty.

I thought as much, and went looking for such a hole on the shaft in the photo I posted, but couldn't find it.

 

Nevertheless, what you write makes sense. I guess I'll have to go and have another look...

 

EDIT: and what docc wrote. I've read all over the place that pulling the shaft apart can be difficult because of a vacuum lock, and putting it back together with too much grease on it difficult for the opposite reason.

[MartyNZ]

On my bike, that hole looks more like an imperfection when it was made, but nevertheless it is necessary.

Old grease gets thicker over years as the oil seeps out, leaving mostly the thickner/soap behind. If possible I try to scoop out or flush out old grease. Your picture appears to show fresh grease, which would be thinner (and better).

[docc]

2 minutes ago, MartyNZ said:

On my bike, that hole looks more like an imperfection when it was made, but nevertheless it is necessary.

Old grease gets thicker over years as the oil seeps out, leaving mostly the thickner/soap behind. If possible I try to scoop out or flush out old grease. Your picture appears to show fresh grease, which would be thinner (and better).

Where is this relief hole to be found? And should it be "maintained?"

[audiomick]

1 minute ago, MartyNZ said:

Your picture appears to show fresh grease,

Yes, it does.

I cleaned out the shaft before I installed it, and only put a very thin layer of grease on the spline. There are enough warnings here about how hard it can be to re-assemble the shaft if one puts too much grease in there that I was cautious, and was relying on the grease nipple for the proper greasing. The grease that came out in the yoke is all fresh.

[audiomick]

13 minutes ago, docc said:

Where is this relief hole to be found?

Very good question, docc. I went looking for such a hole on the shaft in the picture, and couldn't find it.

 

EDIT: I might add that I have a vague memory of having noticed in my childhood just such a relief hole on the drive shafts of various mowers, hay balers and what have you that were designed to be driven from the PTO shaft on the back of a tractor.

 

Watching my father grease those was where I learned how to use a grease gun...

[docc]

9 minutes ago, audiomick said:

Very good question, docc. I went looking for such a hole on the shaft in the picture, and couldn't find it.

I have always thought that space was "sealed."  Caution has always been advised not to over-grease and "hydro-lock" the sliding shaft junction.

Maybe there is a relief "hole" that should be seen to?

[MartyNZ]

1 hour ago, docc said:

Where is this relief hole to be found? And should it be "maintained?"

I looked at one end of the driveshaft in my spare parts box, the one with the grease nipple. It doesn't have a relief hole in it, so I expect that it is in the other end.

I wonder if the "hole" is actually a partially burst disk or frost plug fitted in the end of the shaft. Maybe excess grease has made it's own escape path. 

I think that making sure that old grease is removed,  and a clear relief hole is a good idea.

[Lucky Phil]

I have a brand new drive shaft assembly as a spare and there is no bleed holes. So the yoke and shaft with the splines is one casting with a blanking cap fitted from the yoke end and staked in place. The flat sections you can see are the staking marks. The cap seats on the end of the splines internal end face. I would just clean out the grease thoroughly and drizzle some 5 min Araldite or the resin of your choice down inside the splined section to seal the cap from the inside. a small syringe and 1-2ml of resin. Easy.

 

Phil

[Pressureangle]

Driveshaft spline lubrication is more complicated than it seems it should be, not just ours. 
The main problems are 2; firstly, distributing the grease from the single entry point equally around all the splines. This is usually done by a circumferential groove under the zerk, or as it appears in the V11 shaft by putting the zerk in the endspace where it can find it's way through everywhere. The other problem is the hydraulic one; if you have a relief in the endspace, the grease finds it's way out without going through the splines. The hydraulic action is what drives the lubricant through the splines. On big heavy stuff like trucks, the pressure isn't an issue because the motion is very slow with little travel- by the time it's left the driveway, the shaft has generally gone through most of it's range of motion and made space. On ours, this may not be the case and that first big bump could hydraulic the shaft and um...interfere with suspension movement. My shaft has the zerk in the middle of the splines, and I'm not sure whether it has a distribution groove or not- but I don't grease the zerk anyway, I disassemble the shaft and apply open gear & cable lube manually. That way I'm assured everything is clean and lubed as it can be. So I'm with Phil on the sealing of the yoke end, and after greasing compressing the suspension manually as much as possible to get the range of motion freed up.

[audiomick]

44 minutes ago, Pressureangle said:

...the sealing of the yoke end...

I've been thinking about that. Would it be really tragic if that end of the shaft wasn't air-tight? Phil wrote that the bung in the end is just a plate staked into place. I dare say that isn't really air-tight even when it is new.

I'll be taking mine out again to have a close look at it, but I'm inclined to think that if I don't rely on the grease nipple to lubricate, i.e. take it off every year or two and grease it dismantled on the bench, then it shouldn't really matter too much if that bung doesn't seal 100%.

Or am I overlooking something?